This application claims the priority of German Patent Application, Serial No. 101 56 781.2, filed Nov. 19, 2001, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference.
The present invention relates to a method and device for active compensation of mechanical vibrations and/or deformations in industrial processing machines. The present invention further relates to an industrial processing machine which incorporates the novel and inventive device.
Industrial processing machines, in particular machine tools and robots, require highly dynamic and at the same time highly precise movement patterns. However, both requirements contradict one another because highly dynamic movements generate inertial forces which cause vibrations of the mechanical machine parts. During a material removing process, additional static deformations are encountered as a result of process forces. Both, inertial forces and static deformations, are in particular detrimental when the movement of bulky machine parts is involved and when there is a great distance between the drive motor and the position measuring system, on the one a hand, and the machine point (tool center point in case of machine tools) to be positioned, on the other hand.
Attempts to overcome this problem involve heretofore the use of very rigid mechanical machine components in addition to the use of heavy-duty drive and control units in order to minimize deformations and vibrations as excited by the inertial forces. A mechanical stiffness is normally attained by especially massive (thick-walled) or complicated (ribbed, braced) mechanical elements made of high-strength materials. Apart of the higher manufacturing costs for the mechanical parts, the higher mass is especially detrimental because it contradicts the need of highly dynamic movements and requires drives which must be designed more powerful.
As an alternative to the stiff mechanical construction, the application of so-called gantry machines has been proposed, in which the force generation is distributed within a movement direction over several drives. In this way, the drive forces can be spread more evenly for introduction into the mechanical construction and vibrations can be actively dampened at the attack points of the motor forces. Still, there remains the problem of a great distance between introduction points of the drive forces and the machine point to be positioned. Moreover, a gantry machine requires significantly more complex drive and control units.
It would therefore be desirable and advantageous to provide an improved method and device which obviate prior art shortcomings and which compensate undesired vibrations or mechanical deformations, without increase in the overall mass.
According to one aspect of the present invention, a method for active compensation of mechanical vibrations and/or deformations in industrial processing machines, includes the steps of providing at least one main drive in a primary axis for executing a first motion to move a mechanical machine element and combining the machine element in a secondary axis with an auxiliary drive which executes a comparably more fine-tuned second motion for so moving a machine point of the machine element that the movement of the machine point is composed of superimposed portions of the first and second motions, with the first motion moving the machine point in accordance with a predetermined desired position value, and with the second motion so compensating generated vibrations and/or a deformation of the mechanical machine element that the machine point still assumes the desired predetermined position.
The present invention resolves prior art problems relating to the development of inertial forces as a consequence of highly dynamic movements and thus the excitation of vibration of mechanical parts, by providing an auxiliary drive with small movement amplitude for actively compensating vibrations in the machine point, while still allowing a lightweight construction of the machine parts.
According to another feature of the present invention, the auxiliary drive is supplied with a separate control value which is commensurate with a desired position value and substantially corresponds to a deflection of the mechanical machine element with respect to an ideal rigid mechanical machine element.
Suitably, the control value for the auxiliary drive may be derived by directly measuring the position of the machine element in the machine point to be positioned for determining a vibration and/or deformation of the machine element. As an alternative, the control value for the auxiliary drive may also be derived through a differential measurement between non-vibrating and vibrating positions of the machine point for determining a vibration of the machine element. Another alternative involves an indirect measurement of an actual first acceleration and a pertaining non-vibrating second acceleration in the machine point to be positioned, and a comparison of the first and second accelerations for determining a vibration of the machine element.
According to another general feature of the present invention, at least one of the state variablesxe2x80x94acceleration, speed, positionxe2x80x94of the main drive and the auxiliary drive, may be ascertained, and a respective differential signal can then be derived therefrom for operating the auxiliary drive.
In order to prevent the formation of a vibratory system, it would be beneficial to realize an acceleration measurement at a smallest possible phase loss. In the event of a presence of a phase loss during an acceleration measurement, the phase loss should be suitably compensated.
Since no stationary deflections occur in mechanical machine elements, such as an elastic traverse member, according to another feature of the present invention, a possible direct component of an ascertained relative acceleration may be eliminated through high-pass filtering.
The method according to the present invention is especially suitable for situations in which such a traverse member couples the secondary axis in a mechanically movable manner in parallel relationship to the primary axis.
According to another aspect of the present invention, a method for active compensation of control deviations in industrial processing machines, includes the steps of providing at least one main drive in a primary axis for executing a first motion to move in a secondary axis an auxiliary drive which executes a comparably more fine-tuned second motion for so moving a machine point to be positioned that the movement of the machine point is composed of superimposed portions of the first and second motions, with the first motion moving the machine point in accordance with a predetermined desired position value, and with the second motion so compensating control deviations of the main drive that the machine point still assumes the desired predetermined position.
Thus, the method according to the present invention is also applicable for active compensation of control deviations of the main drive by means of the auxiliary drive.
According to still another aspect of the present invention, a control device for active compensation of mechanical vibrations and/or deformations and/or control deviations in industrial processing machines, includes a first cascade-connected controller structure associated to at least one main drive and including a force controller, a superordinated speed controller and a position controller superordinated to the speed controller, a second cascade-connected controller structure associated to an auxiliary drive and including a force controller, a superordinated speed controller and a position controller superordinated to the speed controller, and at least one distribution unit selected from the group consisting of force distribution unit, speed distribution unit and position distribution unit, and configured to receive an input signal and to deliver an output signal for controlling a one of the controllers of the first cascade-connected controller structure and an equivalent one of the controllers of the second cascade-connected controller structure.
The force distribution unit may be configured hereby to receive as input an actual acceleration value of the main drive and an actual acceleration value of the auxiliary drive, and/or a desired overall force value provided from the speed distribution unit, and to output respective relative acceleration signals for delivery to an input of the force controller of the first cascade-connected controller structure and the force controller of the second cascade-connected controller structure.
The speed distribution unit may be configured hereby to receive as input an actual speed value of the main drive and an actual speed value of the auxiliary drive, and/or a desired overall speed value from the position distribution unit, and to output respective relative speed signals for delivery to an input of the speed controller of the first cascade-connected controller structure and the speed controller of the second cascade-connected controller structure.
The position distribution unit may be configured hereby to receive as input an actual position value of the main drive and an actual position value of the auxiliary drive, and a desired overall position value, and to output respective relative position signals for delivery to an input of the position controller of the first cascade-connected controller structure and the position controller of the second cascade-connected controller structure.
According to another feature of the present invention, there may be provided a high-pass filter for eliminating a possible direct component of the input signal.
According to yet another aspect of the present invention, an industrial processing machine includes a main drive positioned on a primary axis and carrying out a first motion, a mechanical machine element moved by the main drive and including an auxiliary drive positioned on a secondary axis and constructed for executing a second comparably more fine-tuned motion for movement of a machine point to be positioned, a first cascade-connected controller structure for operating the main drive, and a second cascade-connected controller structure for operating the auxiliary drive, wherein the movement of the machine point is a composed of superimposed portions of the first and second motions.
According to another feature of the present invention, there may be provided a traverse member for linkage of the secondary axis in parallel relationship to the primary axis in a mechanically movable manner. In the event of an arrangement of two main drives with two primary axes, a traverse member may be provided for coupling the main drives, wherein the secondary axis is positioned between both primary axes in parallel relationship thereto and supported by the traverse member. Suitably, the auxiliary drive is hereby configured as double-sided linear drive.
Regardless whether the traverse member is provided to maintain a parallelism between the secondary axis and the primary axis or to position the secondary axis between both primary axes in parallel relationship, it is advantageous to so mechanically construct the traverse member as to reversibly absorb support forces required for process forces when the traverse member is deflected.
The present invention resolves prior art shortcomings by allowing the use of lightweight elements with respective vibrations while actively compensating the encountered vibrations by an auxiliary drive with smaller movement amplitude in the machine point to be positioned. Vibrations may hereby be ascertained either through direct measurement of the position or indirectly via an acceleration measurement in the machine point to be positioned. There are many advantages realized by the present invention:
the simple and lightweight construction of the mechanical components results in material saving, simplified manufacture and simplified construction;
as a consequence of the material saving aspect, the moving machine parts of the main drive of the primary axis can be made of weaker construction;
the auxiliary drive travels only a movement path in the millimeter range and is not required to accelerate heavy machine parts, so that the auxiliary drive can be constructed of small size and in immediate proximity of the machine point to be positioned to enable a greatest possible compensation effect;
only the small auxiliary drive is required to control the frequency range of the mechanical vibrations;
control deviations of the more powerful main drive may also be compensated by the small auxiliary drive;
in the event no static deformations (e.g., by weight forces and process forces) have to be compensated but compensation of only vibrations is desired, the vibrations may be detected by acceleration sensors so that the overall mechanical construction is especially simple.